1. Field of the Invention
The present invention relates to a valve control apparatus.
2. Description of Related Art
For example, Japanese Unexamined Patent Publication No. H10-103069A teaches a boost pressure control apparatus, which includes a wastegate valve that opens or closes a wastegate passage of a turbocharger.
As shown in FIGS. 8 to 10B, the boost pressure control apparatus of Japanese Unexamined Patent Publication No. H10-103069A includes a rotatable shaft 102, which supports and drives the wastegate valve 101. A link lever 103 is connected to the rotatable shaft 102, and a rod 105 of a diaphragm actuator 104 is connected to the link lever 103. A valve seat 107 is formed at a wastegate passage 106, and the wastegate valve 101 is seatable against the valve seat 107.
An arrow shown in FIG. 9B indicates a movable range (operational angle) of the link lever 103.
Furthermore, Japanese Unexamined Patent Publication No. 2010-90766A teaches a diaphragm actuator, which drives an exhaust gas bypass valve that opens or closes an exhaust gas bypass passage of a turbocharger.
As shown in FIGS. 11 to 13B, the diaphragm actuator 204 of Japanese Unexamined Patent Publication No. 2010-90766A has a rotatable shaft 202, which supports and drives the exhaust gas bypass valve 201. A link lever 203 is connected to the rotatable shaft 202, and a rod 205 of the diaphragm actuator 204 is connected to the link lever 203. Also, a valve seat 207 is provided at the exhaust gas bypass passage 206, and the exhaust gas bypass valve 201 is seatable against the valve seat 207.
An arrow shown in FIG. 12B indicates a movable range (operational angle) of the link lever 203.
Lately, in many countries, it is mandatory to install an on-board diagnostic (OBD) system for the exhaust gas on the vehicle due to the enhancement of the regulation with respect to the exhaust gas of the engine installed on the vehicle.
Here, in the case where the diaphragm actuator 104, 204 of Japanese Unexamined Patent Publication No. H10-103069A or of Japanese Unexamined Patent Publication No. 2010-90766A is used as the actuator, which controls opening and closing of the wastegate valve 101 or of the exhaust gas bypass valve 201, it is necessary to directly sense the amount of the stroke of the rod 105, 205, as specified by the OBD requirement.
It is conceivable to install a magnetic circuit, which is formed by a magnet(s) and a yoke, to the rod 105, 205. In such a case, a density of a magnetic flux of a magnetic field applied from the magnetic circuit may be sensed with a magnetic sensor. Then, the amount of the stroke of the rod 105, 205 may be obtained based on an electric signal, which is outputted from the magnetic sensor.
In the boost pressure control apparatus recited in Japanese Unexamined Patent Publication No. H10-103069A, the movable range of the link lever 103, which connects between the rotatable shaft 102 of the wastegate valve 101 and the rod 105 of the diaphragm actuator 104, is not clearly taught, and movement of the link lever 103 results in swing motion of the rod 105.
Specifically, when the wastegate valve 101 is driven in an operational range between a full close position (see FIG. 9A) and a full open position (see FIG. 9B), i.e., when a connection 108 between the link lever 103 and the rod 105 is moved along a rotational path (rotational moving path of the link lever 103), which is a curved path having a predetermined radius of curvature about the rotatable shaft 102, the rod 105 is swung by the amount δ (the amount of swing of the rod 105).
Therefore, in the case where the amount of the stroke of the rod 105 is directly sensed with the magnetic sensor, a sensing error may be disadvantageously increased due to the swing motion of the rod 105.
Furthermore, in the boost pressure control apparatus of Japanese Unexamined Patent Publication No. H10-103069A, as indicated in FIG. 10A, a rate of change in the flow quantity of the exhaust gas relative to a change in the amount of displacement of the rod 105 is relatively large in a range located on a full close degree side of a half degree, which is an opening degree of the wastegate valve 101 between the full close degree and a full open degree. In contrast, a rate of the change in the flow quantity of the exhaust gas relative to the change in the amount of displacement of the rod 105 is relatively small in a range located on a full open degree side of the half degree of the wastegate valve 101.
Furthermore, as shown in FIG. 10B, a rate of the change in the amount δ of the swing of rod 105 is relatively small in the entire range from the full close degree to the full open degree of the wastegate valve 101 through the half degree.
Therefore, it is required to improve the sensing accuracy of the amount of the stroke of the rod 105 by reducing the amount of the swing of the rod 105 in the low opening degree range where the rate of the change in the flow quantity of the exhaust gas relative to the change in the amount of the displacement of the rod 105 is largest.
In the diaphragm actuator 204 of Japanese Unexamined Patent Publication No, 2010-90766A, the disadvantage, which is similar to that of the actuator 104 of Japanese Unexamined Patent Publication No. H10-103069A, occurs although a rotation start angle of the link lever 203 differs from that of the actuator 104 of Japanese Unexamined Patent Publication No. H10-103069A, as shown in FIG. 12A.
Specifically, when the exhaust gas bypass valve 201 is driven in an operational range between a full close position (see FIG. 12A) and a full open position (see FIG. 12B), i.e., when a connection 208 between the link lever 203 and the rod 205 is moved along a rotational path (rotational moving path of the link lever 203), which is a curved path having a predetermined radius of curvature about the rotatable shaft 202, the rod 205 is swung by the amount 6 (the amount of swing of the rod 205).
Therefore, in the case where the amount of the stroke of the rod 205 is directly sensed with the magnetic sensor, a sensing error may be disadvantageously increased due to the swing motion of the rod 205.
Furthermore, in the diaphragm actuator 204 of Japanese Unexamined Patent Publication No. 2010-90766A, as indicated in FIG. 13A, a rate of change in the flow quantity of the exhaust gas relative to a change in the amount of displacement of the rod 205 is relatively large in a range located on a full close degree side of a half degree, which is an opening degree of the exhaust gas bypass valve 201 between the full close degree and a full open degree. In contrast, a rate of the change in the flow quantity of the exhaust gas relative to the change in the amount of displacement of the rod 205 is relatively small in a range located on a full open degree side of the half degree of the exhaust gas bypass valve 201.
Furthermore, as shown in FIG. 138, a rate of the change in the amount δ of the swing of rod 205 is relatively small in the entire range from the full close degree to the full open degree of the exhaust gas bypass valve 201 through the half degree.
Therefore, it is required to improve the sensing accuracy of the amount of the stroke of the rod 205 by reducing the amount of the swing of the rod 205 in the low opening degree range where the rate of the change in the flow quantity of the exhaust gas relative to the change in the amount of the displacement of the rod 205 is largest.
Furthermore, in the boost pressure control apparatus of Japanese Unexamined Patent Publication No. H10-103069A and the diaphragm actuator 204 of Japanese Unexamined Patent Publication No. 2010-90766A, if a rod bearing, which slidably supports the rod 105, 205 to enable slide movement of the rod 105, 205 in the axial direction thereof, is provided, there occur some disadvantageous incidents, such as an incident of applying of a large force to the rod bearing, an incident of grinding of the rod 105, 205 against the inner peripheral part of the rod bearing, an incident of localized wearing at the connection between the rod 105, 205 and the rod bearing, and an incident of encountering an operational failure of the rod 105, 205.